1. Field of the Invention
The present invention relates to image forming apparatuses, such as copiers, facsimiles, and printers, and more particularly, to a system and method associated with supplying of developer (e.g., toner) from a developer container to a developing device and replacement of developer containers.
2. Description of the Related Art
A known image forming apparatus includes a photosensitive member serving as a latent image carrier, on which an electrostatic latent image is formed by, for example, a charging device and an exposure device. The electrostatic latent image is developed with developer (developing agent such as, for example, toner), by a developing device, into a visible image.
The visible image is transferred by a transfer device onto a transfer medium (recording medium) supplied from a paper feed cassette, through a paper feed roller and a transport roller, to the photosensitive member. The transfer medium on which the visible image has been transferred is transported by a transport device to a fixing device, where the visible image is subjected to heat and pressure, causing a permanent image to be fixed onto the transfer medium. Then, the transfer medium bearing the permanent image is ejected from the image forming apparatus as a final copy.
The developing device includes a developing sleeve which causes developer to adhere to an electrostatic latent image formed on the photosensitive member, and a developing container in which developer is held. A developer storage device (hereinafter simply referred to as “storage device”) serves as developer storage from which developer is supplied to the developing container.
A bottle (i.e., developer container) attachable to and detachable from the storage device is placed above the storage device such that developer is supplied to the storage device.
FIG. 8 illustrates an exemplary configuration of a bottle, a storage device, and their neighboring components included in an image forming apparatus. FIG. 9 is a cross-sectional view as viewed in the direction of arrow B in FIG. 8. Referring to FIG. 8 and FIG. 9, developer is supplied from a bottle 1 to a storage device 2 through a connecting part (i.e., supply port) 1b located at an end of the length of the storage device 2 and serving as a communicating part. From the storage device 2, developer is supplied across the entire length of the developing device 105. Thus, the bottle 1 and the storage device 2 combine to serve as a supply system for supplying developer to the developing device 105.
The above-described configuration in which developer is supplied from an end of the length of the storage device 2 may cause an uneven distribution of the developer along the length of the storage device 2. Therefore, as illustrated in FIG. 9, a developer evening mechanism 5 serving as an agitator is provided inside the storage device 2 so that the developer from the storage device 2 is supplied across the entire length of the developing device 105. This ensures an even distribution of the developer across the entire length of the developing device 105, and thus can prevent image defects.
Moreover, the storage device 2 further includes a first developer detector 7a, such as a piezoelectric sensor, so as to prevent an excessive supply of developer from the bottle 1 to the storage device 2.
Specifically, when the amount of developer in the storage device 2 decreases, the output of the first developer detector 7a changes. On the basis of this output, a transport mechanism 4 in the bottle 1 is driven to cause developer to be discharged from an outlet of the bottle 1. When the amount of developer in the storage device 2 increases and the output of the first developer detector 7a changes again, the drive of the transport mechanism 4 is stopped. The amount of developer in the storage device 2 thus remains constant.
The storage device 2 also includes a second developer detector 7b to ensure, when the amount of developer in the second storage device 2 is extremely reduced, the capability of transporting developer to the developing device 105 while maintaining an even distribution of the developer across the entire length of the second storage device 2.
In the known image forming apparatus including the developing device 105 and the supply system described above, when the first developer detector 7a detects the absence of developer for a predetermined period of time, a message “Replace the bottle” is displayed on the user control screen (not shown) to inform the user that no developer is left in the bottle 1.
In the supply system having the above-described configuration (discussed in Japanese Patent Laid-Open No. 10-20648), even if the above-described message is displayed on the user control screen, it is still possible to continue the ongoing image formation until the second developer detector 7b determines that no developer is left. When the second developer detector 7b detects the absence of developer for a predetermined period of time, the image forming apparatus terminates (disables) the image formation on the basis of the determination that an insufficient amount of developer remains in the bottle 1 and the storage device 2.
Under the state in which the second developer detector 7b detects the absence of developer, it is difficult to supply developer from the storage device 2 to the developing device 105 in a manner to maintain an even distribution of the developer across the length of the developing device 105. Therefore, after the user replaces the bottle 1 with the new one, a certain period of time for supplying developer from the bottle 1 (i.e., supply operation checking time) is required until the second developer detector 7b detects that the developer is present in the second storage device 2. The initiation of image formation is disabled until the second developer detector 7b detects the presence of developer.
Recently, image forming apparatuses, such as copiers and printers, are expected to perform image formation at higher speeds. This involves a demand for improved productivity that can be achieved by minimizing the time required for supplying developer and paper, performing maintenance operations, and the like.
In a known image forming apparatus, such as that described above, when developer runs out and the image forming operation is stopped, a certain period of time (supply operation checking time) elapses from when the user replaces a bottle (developer container) with the new one until the operation of the image forming apparatus is resumed. Since a high-speed image forming apparatus may require more frequent replacement of the bottle, the time during which the image forming apparatus is stopped may increase and adversely affect the productivity.